Radiofrequency treatments are commonly performed to target painful conditions involving the spine and major joints, but it is often hard to know exactly what the patient has gone through. Let’s demystify.
Ever since Rene Descartes first came up with the theory of pain pathway in 1664, humans have tried to lessen pain by affecting the transmission of nociception to the brain. The idea of neural destruction and interruption of nociception as a treatment of intractable pain was explored in mid-1900s, including surgical laceration of nerves and chemical denervation using phenol.
While still in use in select circumstances, the inherently invasive nature of these techniques and the unpredictable pattern of injectate spread has limited its uptake.
The first documented use of radiofrequency technology for therapeutic neural destruction occurred in 1973, when Shealy targeted the lumbar facet joints, with Cosman and Sluijter bringing the first commercial radiofrequency kit to market soon after.
Since then, with the embrace of radiographic guidance and development of techniques based on cadaveric research by Australian pioneer Nikolai Bogduk, radiofrequency ablative techniques have become accepted as an integral part of interventional pain medicine. More recent uptake of non-destructive pulsed radiofrequency techniques, as well as rise of novel technologies, have broadened its application. So, what are they?
Radiofrequency Ablation (RFA) /Radiofrequency Neurotomy, the “rhizotomy”
Under fluoroscopy or CT guidance, radiofrequency cannulae (needles) are inserted into the region of interest where the afferent nerve fibres, thought to be transmitting pain, are located. These cannulae are electrically insulated except for the exposed tip of 0.5-1cm length.
When the cannulae are connected to an RF generator, continuous AC current is generated, heating the exposed tip in a controlled manner to a temperature that causes tissue coagulation and neural destruction, generally to 80-90 ◦C, for 1-2 minutes. This leads to Wallerian degeneration and interruption of nociceptive transmission, therefore relieving pain.
Studies have shown that application of continuous RF in this manner produces well circumscribed thermal lesions of predictable size, allowing for techniques that can be replicated. This is referred to as Radiofrequency Ablation (RFA)/Neurotomy (RFN), and traditionally called rhizotomy in WA.
Due to its nature, RFA can cause temporary pain flare-ups and is almost exclusively used for nerves without a significant motor component. RFA of medial branch nerves is well validated for treatment of zygopophyseal (facet) joint mediated spinal pain.
Size of thermal lesions and its proximity to target nerves are thought to be vital to the success of RFA. Technologies such as tined RF cannulae and bipolar treatments (generating a contiguous lesion between two cannulae spaced ~1cm apart) have allowed for larger lesion sizes to better capture target nerves, while ongoing refinements in techniques continue, and new potential targets have been identified for pain involving the spine and major joints of the body.
Pulsed Radiofrequency (PRF), a non-destructive alternative
Sluijter and Cosman, brought out this next novel therapy in 1998. While RF ablation uses continuous uninterrupted AC current (and therefore delivery of energy) to heat the RF cannulae tip, in pulsed RF treatments the same AC current is applied in short burst of milliseconds, 2-5 times per second.
This allows for energy delivered to dissipate between pulses and hence allows for treatment without significant heating of tip and associated tissue destruction. The exact mechanism of action of PRF is unclear but thought to be related to the strong electric field created and altered expression of c-Fos gene that may induce changes in neural activity over short-medium term. Pain relief from PRF appears to last in the vicinity of months, whereas a successful RFA may provide benefits for over a year.
PRF technique can be applied to a wider range of targets where neural destruction is undesirable, including major mixed motor/sensory nerves and nerve roots. Temperature is regulated to a maximum of 42 ◦C during PRF to ensure that unintended thermal damage does not occur. Anecdotally it could also be considered as an alternative to RFA in patients whose risk profile would predict significant potential pain flare-up from such treatment.
While the term rhizotomy is sometimes used interchangeably to refer to both RFA and PRF techniques, no tissue lesion is made in PRF and Bogduk emphasises the importance of distinction between the two to minimise confusion amongst patients and colleagues.
Key messages
- Therapeutic radiofrequency technology dates to the 1970s
- Rhizotomy is a generic term used for two different techniques. Distinction is very important
- PRF can be considered in situations where RFA is contraindicated.
The author acknowledges Drs Marc Russo and Rob Wright, whose article on RF technology history was extensively quoted.
– References available on request
Author competing interests – nil